Lawmakers are voicing fresh concerns that jihadists fighting with ISIS in Iraq will bring terrorism back to the United States and other Western countries.

Rep. Mike Rogers, R-Mi., contends that many of the terrorists fighting in Iraq and Syria would likely be able to get back into the U.S. or the European countries they were living in before joining the jihad.

"ISIL has said that they want to take the people who have Western passports -- and remember they are flooding into this country -- thousands of individuals now signing up with ISIL to fight their jihad in Syria and Iraq have Western passports. That's what's so dangerous about this," Rogers told CBS's "Face the Nation."

Rogers said the rise of the so-called Islamic State, also known as ISIS or ISIL, could inspire multiple terrorist groups, including al Qaeda, to see who can strike the West for bragging rights.

"We also know that they want to conduct an attack, but so does al Qaeda. And so now you have two competing terrorist organizations. Both of them want to get their credentials to the point where they can say, we are the premier terrorist organization. Both want to conduct attacks in the West for that reason. And guess what? That means we lose at the end. If either one ever those organizations is successful, we lose," Rogers said.

Sen. Ron Johnson, R-Wi., shares a similar concern about the Islamic State's next objective.

"You know, we had deputy assistant secretary of the state, Brent McGurk, in front of our committee on July 24. He said that ISIL or ISIS is...funneling 30 to 50 suicide bombers into Iraq every month. He said they could easily funnel those suicide bombers into Western nations," Johnson warned on "Fox News Sunday."

"We need to be highly concerned about this. This threat is a gathering storm. It's not going away," he said. "We may be war-weary. But I'll tell you, ISIS, ISIL is not war-weary. They're highly trained; they are highly organized. They have been very patient setting up this caliphate, and their long-term aim really is to use that base of operation against the West."